Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 89. (Budapest 1997)

Vremir, M., Codrea, V. ; Farkas, B.: Trionyx stiriacus Peters, 1855 (Reptilia, Testudines) from the Sarmatian (Middle Miocene) of Minişu de Sus (Romania)

the T. stiriacus group. Recent opinions based on cranial morphology claim that this taxon is, in fact, merely an individual variety of 77. stiriacus (sensu stricto). On the basis of carapacial, and hyo- and hypoplastral morphology, the following differences compared to other members of the Trionyx stiriacus group can be pointed out (HUMMEL 1929, BROIN 1977). Compared to 77. hilberi HOERNES, 1881, several differences regarding the outline of the bony disk and the size of adults are obvious. Also the nuchal, which has a bilobed, strongly enlarged aspect in the case of the piece described in this study is different from that of 77. hilberi, which has an oval outline and is at the same time narrow. In the case of T. petersi, the nuchal is massive and subdivided, similar to the one belonging to the individual obtained at Reghiu. T. peneckei HERITSCH, 1909 has a bilobed nuchal, cranially limited to digitiform apophyses. As in the situation observable in the Mini specimens, some important differences in hyo- and hypoplastral morphology exist. Regarding the morphology of the hyo- and hypoplastra, the well-developed double marginal apophyses, as well as the biométrie relations of these parts, an almost complete identity of MTB 21636/2 and 77. stiriacus (sensu lato) from the French Lower Miocene (Artenay [BROIN op. cit.]) or 77. hoernesi from Styria (HERITSCH 1909) may be noted. However, some differences between the Transylvanian specimens and those mentioned above are apparent in the aspect of the distal section, which exhibits a slight enlargement of the medio-caudal lobe and a disposing of the digited apophysis, respectively. The Transylvanian material makes it possible to reconstruct the morphological and dimensional changes that occurred during ontogeny, beginning with the juvenile (TCM 8377) and ending with the adult stage (MTB 21636). Generally, this process is characterized by the enlargement and ossification of the bony disk surface. In the case of juveniles, the free ends of the ribs surpass the lateral limits of the disk by far. The bony carapace of a semi-adult grows in an increasingly accelerated rhythm compared to the growth of the ribs, a fact which mitigates the size of the free ends that are longer in the caudal part. The relation between the length of the pleural plate and the rib has values of 2/3. The nuchal of the adult is well developed, hypertrophied, and shows typical digited apophyses. A diminishing of the free rib ends can be noticed, their size becoming uniform on the whole circumference of the carapace. In studies of ontogenetic development in Recent trionychids (KORDIKOVA 1991, 1993) it has been highlighted that most of the variations appear on the carapace, especially on its anterior and posterior part, so that different examples of conspecific trionychids, whether or not in the same ontogenetic phase, may have different morphologies. Also in our opinion the complex use of all available characters is the most appropriate clue for identifying fossil soft-shelled turtles. Both the fact that the form and the number of carapacial elements alter during ontogeny, and that there is a considerable inter- and intraspecific variation in the 22 potentially useful carapacial features surveyed by GARDNER & RUSSELL (1994), should be taken into consideration. However, it should be stressed once again that a cladistic analysis of the over 220 fossil trionychid taxa is currently being prepared by MEYLAN (in litt, to FARKAS), and the identification of the three individuals described herein as Trionyx stiriacus is tentative at best. Whether 77. stiriacus in itself is a bona fide species, or is nomenclaturally preoccupied remains to be investi-